Waterproofing and Insulating a Concrete-Block Walls
benneaf3
| Posted in General Questions on
What should I use as a water barrier/air barrier on a house with external walls of concrete block? Fluid applied (Drylock?)? Tyvek? Can I insulate the walls on the exterior AND the interior? (We are going to have to put up some framing to run wire through as we re-wired.) I’m thinking Rockwool batts inside and foam outside. Thank you
Andrew
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Andrew,
That depends on a few things. This sounds like a retrofit - what are the layers that are currently in place, and what type of siding do you plan on using?
Current layers, inside to outside...cheap paneling, block, furring strips, aluminium siding. I don't think there is currently any insulation on the exterior.
My plan is to year off the interior paneling, frame 20" OC, insulate with Rockwool, and sheet rock over that. In the outside eventually I'll tear off the aluminum siding, insulate with foam boards, and then likely vinyl siding.
I would flip the build around. Insulating with batts against masonry is risky in most cold climates. Take care of the outside, then insulate on the inside.
You want a proper WRB over the CMU. Could be one of the fluid applied ones rated for concrete (Drylock is not a WRB) or can be standard house wrap. You can also put the house wrap over the foam and add small window bucks. This would keep your drainage in a single plane which would make your flashing details much easier.
Once the outside is insulated and the flashing details are done, you can insulate to your hearts content on the inside without any worries. You still need make sure to follow the insulation ratios in the Table 2 here, your exterior rigid need to match the fluffy you are installing based on your climate:
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-100-hybrid-assemblies
I'm in East Tennessee close to Knoxville...not a really cold climate territory. (zone 4 I believe). Given the parameters of my project it's just impossible to turn things around. The wiring has to be redone and there's literally no chases. The current wiring is either above the ceilings, or in conduit....or not in conduit.
My plan is to frame all the external walls and use them as chases for wiring and possibly some plumbing. Then insulate with rockwool. Another detail I don't know is if I should use faced batts or unfaced and if I need any other kind of smart barrier on the inside face of the insulation.
Concrete block construction is one of the few cases where EIFS is a good choice for exterior finish. It provides continuous insulation on the exterior as a part of the system and from an overall system standpoint, it is a mid-priced system. You would use a fluid-applied VR/WRB that is specified as a part of the system. The notorious moisture issues with EIFS are mostly on wood-frame construction. These systems were designed for use on masonry construction, and a little bit of leakage won't bother the masonry at all. But with proper installation, there shouldn't be any leakage. All of the manufacturers publish a wide range of details for any typical terminations and penetrations. Make sure your contractor follows all of these details and other installation instructions.
I dont' have the budget for EIF's (at least I don't thing so). This is just a small rental house. I'll put it together as well as I can, but I'm on a tight budget.
Once you've decided to install a fluid-applied WRB and exterior (or interior) insulation, you've spent about 3/4 of the cost for an entire EIF system. If you then look at the marginal cost of installing furring and vinyl vs. the cost of the mesh and stucco coating, I think you'll find that they are about the same. It's worth considering, anyhow.
If going with exterior you need to consider air leakage at the top of the wall (and to some extent to bottom joint with foundation) since the blocks are hollow. You can insulate all you want on the outside but if you don’t stop the air movement at the top, you will achieve nothing.
Good reminder. We'll have all the sheetrock down inside..actually, currently it's just paneling attached directly to the block. I'll air seal all I can while it's down.
Here's some useful information if you go the fluid WRB route:
Liquid-Applied Water-Resistive Barriers.
Thank you